The present invention relates to a fixed material (i.e., medium) transportation apparatus, a liquid fixing apparatus having the transportation apparatus, and a sucking unit of a fixed material in the liquid fixing apparatus, and more particularly to a technique for sucking and holding a fixed material in the liquid fixing section of the liquid fixing apparatus.
In an ink jet printer or an ink jet plotter which is one of liquid fixing apparatuses, for example, there has conventionally been employed such a structure that a recording medium to be a fixed material is fed into a recording section by means of a paper feeding roller and is then discharged with pressing by means of a paper discharge roller (a driving roller) and a spur roller to be a driven roller. FIGS. 31A, 31B and 31C are views extracting only a recording section in the ink jet printer and the main part of the transportation apparatus of a recording medium.
More specifically, in such an ink jet printer, a recording medium 1 is fed into a recording section 4 by means of a paper feeding roller 2 (and a driven roller 2a) and is then discharged with pressing by means of a paper discharge roller (a driving roller) 6 and a spur roller 6a to be a driven roller as shown in FIG. 31A. In this case, the pressing force of the spur roller 6a is set such that a damage (a spur mark) is not left on the recording medium 1.
In the ink jet printer having the transportation apparatus of a recording medium shown in FIG. 31A, however, in some cases in which an image having a large number of ink particles discharged, for example, a solid image is to be recorded in the recording medium 1, the recording medium 1 absorbs a large amount of ink and is swollen like a wave toward the recording head 8 side as shown in FIG. 31B, that is, so-called cockling is generated.
When the cockling is generated, a space between the recording medium 1 and the recording head 8 is reduced so that the flight distance of the ink particles is varied, resulting in a recording unevenness or the recording medium 1 comes in contact with the recording head 8, causing a dirt. Also in the transportation apparatus of the recording medium shown in FIG. 31A, if a span between the paper feeding roller 2 and the paper discharge roller 6 is comparatively short, it is also possible to prevent the drawback as much as possible by keeping the cockling within a permissible range.
In the inkjet printer, however, it is necessary to increase the number of nozzles for a nozzle train having each color or to arrange a nozzle train having a plurality of colors in the transportation direction of the recording medium in order to further increase a recording speed in the near future. In these cases, the dimension of a recording head is increased in the transportation direction of the recording medium 1 as shown in FIG. 31C. If the length of the recording medium 1 is increased, the span between the paper feeding roller 2 and the paper discharge roller 6 is also increased. In such a structure that the recording medium is to be delivered and discharged with an interposition between the paper feeding roller 2 (and the driven roller 2a) and the paper discharge roller 6 (and the spur roller 6a to be the driven roller), therefore, the cockling cannot be prevented at all and the permissible range is exceeded. In an ink jet printer having a large head length, it is also possible to suppose a structure in which the recording medium is delivered and discharged with an interposition between two sets of rollers cannot be formed depending on a type.
Moreover, the cockling is comparatively small when a special paper of the ink jet printer is used for the recording medium, and is large when a plain paper is used. For this reason, in the design of the ink jet printer, a paper gap [a space A between the recording medium 1 and the recording head 8 in FIG. 31A] is usually increased in consideration of the floating portion of the plain paper due to the cockling when the same paper is used. If the paper gap is thus large, flight curving is caused over the ink particles discharged from the nozzle of the recording head and a shift of an impact point is increased correspondingly even if the special paper requiring no increase in the paper gap is used. Thus, there is a possibility that an enhancement in printing quality might be prevented.
Furthermore, when the recording medium 1 is floated by the cockling, the floating recording medium 1 is pushed against the spur roller 6a as shown in an arrow B of FIG. 31B. As a result, a spur mark is left on the recording medium 1 by the spur roller 6a as shown in FIG. 32. The spur mark is particularly remarkable over the plain paper having large cockling, causing a deterioration in the printing quality.
On the other hand, in recent years, there have been variously proposed structures in which a hollow-box shaped sucking section is mainly provided on the transportation surface of a recording medium and the recording medium is sucked by a sucking pump through a plurality of sucking (through) holes provided in the sucking section (see Japanese Unexamined Patent Publication Nos. JP-A-63-303781, JP-A-3-270 and JP-A-2001-347710). Some of them have proposed a structure in which a recording medium is sucked into a platen through the sucking holes as a cockling eliminating device.
However, all of them have the structure in which the through hole is simply opened in the hollow-box shaped sucking section to carry out the suction, and it is hard to prevent the cockling over the whole surface of the recording medium in the recording section. Moreover, a portion protruded from the recording section of the recording medium floats and is thus pushed against the spur roller 6a as shown in an arrow B of FIG. 31B. As a result, it is impossible to prevent a spur mark from being left in the recording medium 1.
In the conventional examples described in the publications, furthermore, there has been employed a structure in which the through hole is simply opened in the hollow-box shaped sucking section to carry out the suction. Therefore, if sucking force is too large, precision in transportation (paper feeding) might be deteriorated. For this reason, under present conditions, practical use cannot be realized except for a partial large-sized printer to carry out paper feeding in the direction of a gravity (utilizing a self weight of a paper for the paper feeding).
In recent years, moreover, so-called frameless printing has been carried out in the ink jet printer. There has been a problem in that a so-called waste ink mist is generated in which ink particles supplied from a recording head do not impact on the recording medium but the transportation surface of the recording medium at the outside of the peripheral edge of the recording medium. When such a waste ink mist sticks onto the transportation surface of the recording medium, the back face of the recording medium is made dirty. Therefore, there has conventionally been known a structure in which a mesh screen is provided in this region as described in JP-A-8-169155, for example. In such a structure, however, the ink particles discharged toward the mesh screen partially pass through the mesh screen and partially collide with a frame body constituting the mesh screen, thereby generating a floating mist.
Moreover, in some cases, a harsh sucking sound is generated on various conditions if the sucking holes are provided. Therefore, there has been proposed an ink jet printer comprising a system for coupling a silencer to the discharge port of a sucking pump and eliminating a sound generated by the sucking pump through the silencer (see JP-A-2001-239680).
However, by providing the silencer on the downstream side of the sucking pump in the ink jet printer, a component cost, an assembly cost and an installation space for the silencer are increased. For this reason, there is a problem in that the ink jet printer itself becomes expensive and large-sized.